1. Field of the Invention:
This invention relates generally to a D.C. motor and more particularly to a D.C. motor operating without a brush and commutator, except during start up.
2. Description of the Prior Art:
D.C. motors have commonly used brushes to supply direct current to the coils of the motor. This motor is preferably used since it generally is smaller than an induction motor and yet generates a larger force and uses less current. Unfortunately, the use of brushes causes noise problems and since it is impossible to make the contact between the commutator and the brush perfect, there often appear sparks at the contact point. These sparks cause wear on the brushes and the brushes must hence be replaced.
Due to the mechanical complexity necessary for this type of connection, as well as the fragility of the delicate parts, such a motor experiences many maintenance problems during its operation. Accordingly, it is impossible to expect the motor to run continuously without some repairs. Further, due to the lack of stability of the current supplied through the brushes the rotational speed of the motor varies somewhat. Thus, the motor cannot be used where a precise speed is demanded.
Other motors have been devised which do not use the brush and commutator arrangement, but rather sense the position of the rotor and change the fields on the driving coils in response thereto. The sensor used may be photoelectric or some form of sensing coil, which in any case do not make physical contact with the rotor. While these devices avoid the problem of noise from the brushes they are not completely reliable especially in the starting operation.